The most common and most likely answer to this crossword clue is the 8 letter word MISSPOKE
I've seen this crossword clue in The Guardian
M
I
S
S
P
O
K
E
More clues leading to the result MISSPOKE
Buddy explains!
The straight part
We know that "failed to deliver clear message" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case failed to deliver clear message = misspoke.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MISSPOKE mean?
MISSPOKE verb- To fail to pronounce, utter, or speak correctly.
- To speak insultingly or disrespectfully.